The present invention relates to an apparatus for dampening the noise produced by pneumatic devices and, more particularly, to a flexible dampening apparatus which touches the housing of the pneumatic device and which permits movement of the diaphragm of the pneumatic device to control the output pressure and to dampen noise.
Typical pneumatic devices which may, for example, provide an output pressure in response to a sensed condition to control a load such as a pneumatic motor comprise a housing having at least two chambers divided by a diaphram. One of the chambers contains a nozzle which acts in cooperation with the diaphragm to control the output pressure from the pneumatic device. Typically, a source of main pressure is connected through a restriction to the chamber in which the nozzle is located. As a rule, the restriction which connects the source of main pressure to the pneumatic device is greater than the restrictions in the branch or output line. As a result, a searching condition, wherein the diaphragm will continually move closer and then farther away from the nozzle, will exist. The diaphragm is unable to find a stable position with respect to the nozzle at which the restriction between the diaphragm and the nozzle will balance the restriction in the main line and the restriction in the branch line. This searching condition is characterized by an audible hum.
Prior art devices have attempted to eliminate this audible hum or noise by placing steel balls in one of the pneumatic device chambers. The balls provide damping action by adding an impulse energy to the pusher plate between diaphragms in the pneumatic device at non-harmonic intervals to the frequency caused by the hum. However, such a device with steel balls therein depends on gravity and, therefore, proper mounting position. Another method to dampen noise is to apply grease to the pusher plate. This grease makes contact with both the pusher plate and the wall of the housing of the pneumatic device and adds resistance to high frequency movement. The use of grease is, however, too highly operator sensitive for proper application.
The present invention provides adequate damping without the problems of the prior art methods by utilizing a flexible pusher plate or disc which makes contact with the wall or walls of the pneumatic device to thereby dampen the vibration energy of the diaphragm and to eliminate audible hum.